The fact that the visual performance of a human eye depends on the ambient conditions is known. In particular, both the ambient illumination and the contrast of the observed object influence the visual performance. As an example for the influence of the ambient illumination, the phenomenon of night myopia, that is, shortsightedness under mydriatic conditions, is mentioned. The contrast sensitivity in turn depends on the spatial frequency of the observed object. Thus, for example, FIG. 2 in U.S. Pat. No. 7,771,052 shows a typical profile of the contrast sensitivity over the spatial frequency, specified in cycles per degree (cpd).
What is common to both phenomena is that they influence the visual performance of different persons in different ways. That is to say each individual has different sensitivity toward the ambient illumination and the contrast.
Instruments and methods have been developed very recently which allow the refraction of the eye to be established individually, taking into account different ambient conditions. Thus, for example, Carl Zeiss Vision GmbH has under the name iProfiler made commercially available a measuring instrument for determining the objective refraction; this calculates prescriptions according to the so-called iScription method. The latter method takes into account different ambient conditions when calculating the refraction values for the spectacles prescribed to the ametropic person. United States patent application publication 2010/0198817 A1 teaches the establishment of a subjective refraction and a plurality of objective refractions for a multiplicity of different boundary conditions, such as brightness, contrast, et cetera. An effective objective refraction is then determined from the plurality of objective refractions. The effective objective refraction is then compared to the objective refraction and the deviations are determined. The intended values for the spectacle glass are then determined from the effective objective and the subjective refraction.
In both cases, the prescribed effect of the spectacles is calculated from a—possibly also weighted—averaging over different conditions. It therefore constitutes a better or not so good compromise.
The prior art has also disclosed so-called electro-active elements. United States patent application publication 2008/0180630 A1 describes an element that can, for example, be switched between a first optical effect and a second optical effect. In order to produce the first optical effect, the element is in a deactivated state, that is, the voltage(s) applied to the electrodes is (are) below a threshold. In order to produce the second optical effect, the element is in an activated state, that is, the voltage(s) applied to the electrodes is (are) above a threshold. The optical effect of the electro-active element can also be embodied in a “tunable” fashion.
Furthermore, this document describes an electro-active lens for correcting presbyopia. The near part and optionally the progressive part of the lens are configured to allow the electro-active effect to be switched in order to correct the missing or adversely affected accommodation ability of the eye when required.
United States patent application publication 2007/0280626 A1 and WO 2008/002388 A2 describe electro-active lenses that are equipped with a distance sensor in order to be able to adapt the refractive power of the lens automatically to different object distances.
For ophthalmological applications, the refractive power of the above-described electro-active lenses is set purely in respect of the desired object distance(s). No other parameters are considered.
DE 102 39 689 A1 describes a spectacles arrangement with an adaptive lens, in which radiation reflected by the eye is detected and the refractive effect of the lens is modified locally depending on the detection signal. This results in adaptive spectacles, which undertake the adaptation for the object observed by the eye and, in doing so, at the same time correct possible refractive errors by the eye. Extremely high technical complexity is required in order to ensure the desired function.